Unit III: DNA and Inheritance

Gene Mutations

Fig. 25.2

Tortoiseshell Cat--gene expression

--only females (X-linked)

“Stormy”

Gene Mutations--any change in gene sequence--

HOW DO THEY HAPPEN??

Errors in Replication: rare; DNA Polymerase “proofreads” and corrects mistakes

Mutagens: low rate; environmental influences (UV radiation, certain chemicals); DNA repair enzymes fix damage

Transposons: “jumping genes”; specific sequences of DNA that can change locations on chromosomes

FIG. 24.16

Transposons

Indian Corn

Types of Mutations

•FRAMESHIFT--insertion or deletion of a nucleotide; changes how the triplet code is read;

•THE CAT ATE THE RAT•THE ATA TET HER AT (“C” REMOVED)

•POINT MUTATION--substitution of one nucleotide for another

silent--codes for same amino acidnonsense--codes for “stop”missense--changes amino acid and shape

FIG. 26.13

Sickle Cell Anemia

•Point Mutation(single nucleotide)

•Changes shape ofhemoglobin (HB)

•HB forms stiff rods•Can’t carry O2

Fig. 26.2

Nondisjunction in Meiosis=change in chromosome #

3 chromosomes

Fig. 26.1

EXTRA CHROMOSOME--Trisomy 21

•Down Syndrome

•Nondisjunction

•Affects all cells

Fig. 26.3.b1

TRISOMY 21-Gart gene

Gart gene

Fig. 26.4

XO XXY

TURNER SYNDROME KLINEFELTER SYNDROME

Abnormal Sex Chromosome Number

FIG. 26

Muscular Dystrophy--X-linked

Fig. 26.5

Gene Deletion--Williams Syndrome

Fig. 26.6

Duplication and Inversion--”inv dup 15” syndrome

Fig. 26.7

Translocation--chromosomes 2 and 20 (Alagille Syndrome)

Two non-homologous chromosomes exchange segments

Fig. 26.8

Inversion (during Meiosis)